Its inhabitants are human, but so isolated that they are unable to grasp the existence of other worlds besides their own. Outsiders must be demons. Earth is a place that exists only in legend, in the tales of their ancestors. But time is running out for this forgotten civilization... their world is being pulled straight towards the center of a galactic whirlpool, two orbiting black holes in space.

Can Kirk convince them to trust him, before their world is destroyed for ever?

In his book The Trouble with Tribbles, in which author David Gerrold tells how the popular episode of that name came to be written, he mentions that his very first Star Trek story, written after watching the show's premiere in September 1966, was a sixty-page outline for an ambitious two-part episode which he called "Tomorrow Was Yesterday". In it, the Enterprise stumbles across Voyager, a generation ship launched from Earth centuries before. Voyager is being drawn into a nearby star, and the Enterprise crew have to convince her inhabitants to restart her engines and change her course. Their mission is complicated by the fact that a long-ago mutiny on board Voyager has left the inhabitants divided into two warring factions, one controlling the command center, the other controlling the engines, with both groups having forgotten that they're inside a spaceship.

Producer Gene L. Coon rejected "Tomorrow Was Yesterday", but was so impressed by it (and possibly by the fact that he received it within weeks of the show's premiere) that he invited Gerrold to meet with him, and eventually submit more story premises. Gerrold did so, and one of his premises eventually became "The Trouble with Tribbles". In the meantime, Gerrold took the outline for "Tomorrow Was Yesterday", removed all the Star Trek-specific references, and turned it into a film script called Yesterday's Children. When the script didn't sell, he began turning it into a novel, which wound up being about a battle between two starships rather than an encounter with a generation ship. Gerrold succeeded in selling the novel version of Yesterday's Children, which was published in July 1972, and which eventually served as the launching pad for his "Star Wolf" novel series.

Meanwhile, Bantam Books, which had been publishing novelizations of the Original Series episodes since 1967, began publishing original Star Trek novels in 1976. Gerrold agreed to produce an original novel for Bantam, and went back to the original sixty-page outline for "Tomorrow Was Yesterday" for the story, which became the novel The Galactic Whirlpool.

Canon characters listed below are linked to the main article about them. Non-canon characters are not linked, but those that recurred, appearing or being mentioned in more than one story, are defined further in Bantam TOS characters.